Shock hydrodynamic analysis and shadowgraphic measurements of laser-ablated carbon-reinforced silicon carbide

Shadowgraphic measurements of pulsed laser ablation of a C/SiC target at laser energies from 50 to 110 mJ and ambient pressures of 100 and 760 Torr were performed to study ablation shockwave dynamics. Laser shadowgraph images of the expanding shock front between 0.1 and 10 µs after the ablation were used to characterize the hydrodynamics of the shock front and shock-heated gas flow using Sedov-Taylor theory and Rankine-Hugoniot relations. The shockwave transitioned to an acoustic wave around 5-6 µs, limiting the validity of the Rankine-Hugoniot relations to this range of delay times. The shock expansion and Sedov-Taylor fit coefficients were used to calculate the initial blast energy as well as the energy expended on the laser-target interaction. This energy was used to calculate an upper estimate of the mass ablated by the laser across all experimental conditions. A maximum mass removal of 0.568 µg was calculated for a 110 mJ pulse at atmospheric pressure. Increasing the ambient pressure was found to have a minimal effect on the amount of mass ablated; this is attributed to the effects of inverse Bremsstrahlung coupling between the 1064 nm probe laser and the plume, limiting the amount of laser energy deposited directly into the target.